Purist mode has disappointed me due to my preconception that it was going to make Absolution more like how Hitman traditionally played.
Instinct and the on-screen threat detector have become such pivotal elements in Absolution that activating purist mode makes it almost impossible to get anywhere without being detected. Things like being able to:
see your enemies through walls
their patrol paths
who is suspicious of you
your mini-map on-screen
are meant to be a replacement, or at least a more immediate visual representation, of the highly integral map screen of previous Hitman games, as well as the suspicion indicator and compass. By removing all of these HUD elements in purist mode, Absolution truly does become an exercise in blind trial and error.
Now, I raise that last underlined point because people often argue that trial and error is what Hitman has always been, but they are completely wrong. In comparison to Absolution's purist mode, professional mode in previous Hitman games still showed your HUD and allowed access to the map, because it really would have become trial and error if this weren't the case. So difficulty stemmed from being able to navigate through the level, the timing of the guards and distractions, and essentially how well you could manipulate the AI on a macro level. Therefore, the concept of being a skillful Hitman player was more about being a timelord who could always be in the right place at the right time through intricate planning. If you watch speed runs of silent assassin rank and/or professional mode on Youtube, you will see an almost artistic precision in how these players tackle the level - it's basically a type of strategy game in a stealth action game's clothing.
In Absolution, purist mode shifts the focus of difficulty from this macro level planning of old Hitman games, down to the micro level of individual interactions with enemies ala MGS, Ass Creed or Splinter Cell, which isn't nearly as satisfying in the grand scheme of things. Ultimately, the idea of purist mode feels comparable to increasing the difficulty in Splinter Cell: Conviction to make it "more like old Splinter Cell" - it doesn't suddenly make it more like the old games, it simply makes the new gameplay systems much more difficult to cope with. Taken as a difficulty setting, purist is apt because yes it does make it extremely fucking hard, but in no way does it fundamentally change Absolution to make it more like older Hitman titles. There is really nothing "purist" about it in that sense.